Motion search method and apparatus for minimizing off-chip memory access

Abstract

A motion search method and apparatus for minimizing an off-chip memory access to reduce cycles for predicting a motion vector. A sum of absolute differences (SAD) calculation processing is performed, while an off-chip memory is accessed using Direct Memory Access (DMA). A position of a current macro block is determined if a frame is input and the length of a horizontal search line is set according to adjacent motion vectors and predetermined external parameters. The SADs are calculated by calculating medians of the adjacent motion vectors as a predictive motion vector, setting a vertical direction value of the predictive motion vector as an initial search line, and sequentially searching at least one horizontal search line, and determining a position of a minimum SAD from the at least one horizontal search line. The minimum SAD position is selected as a final motion vector.

Description

CLAIM OF PRIORITY[0001]This application claims the benefit of priority under 35 U.S.C. § 119(a) from a Patent Application filed in the Korean Intellectual Property Office on Jan. 26, 2007 and assigned Serial No. 2007-08387, the contents of which are incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates generally to media processing of motion prediction for image compression technology. More particularly, the present invention relates generally to a motion search method and apparatus for minimizing an off-chip memory access.[0004]2. Description of the Related Art[0005]In the case of digital image data used in many applications, including but in no way limited to video conferencing, High Definition Television (HDTV), Video On Demand (VOD) receivers, Personal Computers (PCs) supporting Moving Picture Experts Group (MPEG) images, game tools, terrestrial digital broadcasting receivers, digital satell...

AI Technical Summary

Benefits of technology

[0022]An exemplary aspect of the present invention is to solve in part at least some of the above problems and / or disadvantages and to provide at least the advantages described herein below. Accordingly, an exemplary aspect of the present invention is to provide a method and apparatus for increasing a search speed by adaptively setting the size of a horizontal search line by referring to adjacent motion vectors while using a search pattern of a Predictive Line Search (PLS) method, reading reference memory data of a horizontal line using a memory access method, such as Direct Memory Access (DMA), enabling parallel processing of a memory access and a SAD (sum of absolute difference) calculator, and significantly reducing an off-chip memory access by processing the reference memory data of the horizontal line in an on-chip memory.

[0023]According to one aspect of the present invention, there is provided an exemplary motion search method for minimizing an off-chip memory access in memory access processing and SAD (sum of absolute difference) calculation processing, wherein an off-chip memory is accessed using Direct Memory Access (DMA) while SAD calculation is performed, the method may typically comprise: if a frame is input, determining a position of a current macro block and setting the length of a horizontal search line according to adjacent motion vectors and predetermined external parameters; calculating SADs by calculating medians of the adjacent motion vectors as a predictive motion vector, setting a vertical direction value of the predictive motion vector as an initial search line, and sequentially searching at least one horizontal search line; and determining a position of a minimum SAD from the at least one horizontal search line, and if the minimum SAD is located on the center line of the at least one horizontal search line, ending the motion search and selecting the minimum SAD position as a final motion vector.

Problems solved by technology

Although high coding efficiency has been achieved by eliminating temporal redundancy in moving picture encoding, due to the fact that a motion search needs the largest amount of computation for performing moving picture encoding, the ability to process the motion search quickly becomes an important technical problem.

In addition, the FSBMA needs a great amount of computation due to a high memory bandwidth and a frequent SAD calculation, if the FSBMA is applied to hardware without any change, because many Processing Elements (Pes) are needed for real-time implementation.

However, these methods have many problems with implementation in a media processor and / or hardware for performing SAD computations at high speed because complex judgment sentences and abnormalized data are referred to in order to reduce the number of search points.

However, the aforementioned conventional motion search methods have a drawback in that it is easy to obtain a local minimum value in an image having a complex and great motion, thereby resulting in a degradation of image quality and degradation of a compression ratio.

On the other hand, there are many cycles needed to access a reference image stored in an off-chip memory.

However, in conventional high-speed motion search methods a subsequent search point is dependent on a current search result, (such as the diamond search method), and therefore data of the subsequent search point cannot be obtained in advance.

Therefore, there is a great deal of difficulty in implementing the conventional high-speed motion search methods as a media processor or by other hardware, and such methods have a relatively complex control command structure.

However, there is a problem with the PLS method as it sets a horizontal line size to a horizontal size of a search window for all macro blocks, frequently causing the occurrence of unnecessary off-chip memory access even for images having a small motion, blocks having high correlations with motion vectors of adjacent blocks, and background images.

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